Magnetic field sensitive devices are used to measure magnetic fields. Examples of magnetic field sensitive devices are Hall effect devices. Hall effect devices have an output signal proportional to the magnetic field. At a magnetic field of zero, magnetic field sensitive devices may output a signal which is different from zero. This signal is called the offset error (=zero field error) of the device.
Hall effect devices comprise a Hall effect region where the Hall effect takes place, which is sometimes called active region, and which is provided with three or more contacts. Generally, the Hall effect region is formed of a semiconducting material in a semiconductor substrate. A contact may be formed by a contact tub located in or in touch with the Hall effect region. A contact may be made by a contact diffusion or an implantation process. Several contacts may be connected via metal lines to the same terminal, such as in an interconnect layer of the semiconductor technology. Terminals are used to supply the device with electric power and to tap its output signals
Hall plates (sometimes called Horizontal Halls (HHalls)) are flat devices and may have thicknesses 5 to 10000 (typically 50) times smaller than their lateral size. They are used to detect magnetic field components along their thickness direction (i.e. direction into the semiconductor substrate). In silicon technology, Hall plates are typically 1 to 3 μm thick and 10 to 100 μm large in lateral directions. Their layout can be rectangular, square, circular, octagonal, cross-shaped, or even triangular.
Vertical Hall effect devices (VHalls) are stout devices in which one of the lateral dimensions is comparable (0.2 times up to 10 times) to their dimension in the thickness direction (i.e. direction into the semiconductor substrate). VHalls often have the shape of long stripes, mostly straight, sometimes curved, arc-shaped, or even circular ring shaped. VHalls are used to detect magnetic field components parallel to the semiconductor main surface.
Hall effect devices with four terminals may be operated in a spinning current operation, where, in a first operating phase, current is sent through a first pair of terminals and voltage is tapped at a second pair of contacts, and, in a second operating phase, the first and second pairs of terminals are swapped and finally the voltages of both operating phases are combined (added or subtracted) to a total signal. The zero field error of this total or overall signal may be called residual offset. Expressed relative to the magnetic field (equivalent magnetic field) it may be about 500 times smaller than in each individual operating phase.
Several Hall effect devices comprising three terminals are known and an offset cancellation operation for a series connection of several Hall effect devices comprising three terminals has been described. The offset cancellation operation includes a number of operating phases, wherein coupling of the contacts of the Hall effect devices to the terminals is different in different operating phases. The output signals obtained in all operating phases are combined into a total signal and the offset in the total signal is also called residual offset.
The residual offset generally depends on the supply voltage at which the device is operated. With larger supply voltages the residual offset grows. This is caused by a self-heating and an electrical non-linearity of the devices, wherein these effects are larger at larger supply voltages. In order to achieve a low residual offset the devices may be operated at a low supply voltage of e.g. 0.5V (instead of larger supply voltages of 2 . . . 3V). However, sensor circuits and sensor control circuits often operate at supply voltages of 3 to 5V. A bias circuit may be provided to control the supply voltage. By using a bias circuit, the control circuit may waste a lot of voltage. If the external supply voltage is 3V and the Hall effect device is operated at 0.5V, the control circuit wastes 2.5V, which is 5 times the power of the Hall effect device. In such a case, the power efficiency of the sensor is only a sixth.
A vertical Hall sensor with series-connected Hall effect regions has been described, in which current flows through several devices in series. Thus, each device is operated at a lower supply voltage and this may result in a better residual offset. For devices with four terminals this is straightforward, however, for devices with three terminals this is not straightforward.